Unlike a heat curdling protein such as globulin, albumin or the like, casein which is a main component of a milk protein has heat softening properties. Due to such properties, it is extremely difficult to produce a food product such as, for example, an artificial meat product containing casein or a milk protein as a main component thereof and having a texture which can be subjected to heat cooking because its texture is liable to be spoiled by heating.
Accordingly, various methods have been heretofore proposed to modify heat softening properties of casein. For example, a method in which a milk protein is formed into fiber and boiled in a salt bath or treated with a compound having an aldehyde group to give resistance to heat softening (Schmandk et al, Die Nahrung, 20, 10, 911-914 (1976); or Japanese Patent Publication No. 26381/1981); and a method in which milk protein is formed into fiber and treated with an aqueous phosphate to give resistance to heat softening (Japanese Patent Laid Open Publication Nos. 79048/1977 and 79049/1977) have been known. However, resistance to heat softening resistance provided by these methods is not always sufficient, and in any case, a milk protein is previously fixed in a predetermined shape such as a fibrous form and then the shaped protein is treated to give resistance to heat softening. Therefore, the protein can not be finished in a desired optional shape. Further, a method which comprises treating a solution containing casein with a protease, a phosphate and a multivalent metallic compound to gel the solution and then heating the gel to give heat curdling properties has been also known (Japanese Patent Publication No. 32857/1983). However, since this method provides heat curdling properties to the protein by gelation and heating, the protein can not be finished in a desired optional shape, either.
The present inventors have intensively studied modification of heat softening properties of casein. As the result, the present inventors have found that, when an aqueous solution or dispersion containing casein and an acidic polysaccharide is heated under certain conditions and the resulting heated product is formed into a desired shape and treated with a multivalent metallic compound, the heat softening properties of casein can be readily modified and, in addition, the products can be finished in a desired optional shapes.